Today marks the start of the busiest travel period of the year, as far-flung families gather for Thanksgiving, and tourists and native New Yorkers alike descend on Manhattan for Macy’s famous Thanksgiving Day Parade.

The weather forecast calls for rain or snow tomorrow for the 79th annual parade, in which six new floats and four new giant balloons are expected to join the three-hour march down Broadway and just past Herald Square. The parade begins at 9 a.m. and is scheduled to end at noon. It will be broadcast on Channel 4.

Among the 14 giant balloons will be the new Dora the Explorer, a Nickelodeon cartoon character that is one of America’s top-rated cartoons, along with SpongeBob SquarePants.

“When the kids see Dora, there is going to be a roar,” a spokesman for Macy’s, Orlando Veras, said.

A giant Scooby-Doo balloon will lead the procession, marking the cartoon dog’s first appearance in the parade.

“Everyone is surprised when we say that this is his first time,” Mr. Veras said.

The noted New York sculptor Tom Otterness has designed a Humpty Dumpty balloon for the parade, the first artist-designed balloon the parade has ever featured.

While most renditions of Humpty Dumpty depict him sitting on his wall, Mr. Otterness’s balloon shows the famous egg upside-down in mid-fall.

Macy’s estimates that 2.5 million people will watch the parade from the streets, Mr. Veras said. The balloons will be inflated today, and the process is viewable from 3 to 10 p.m. on West 77th and West 81st Streets.

The weather today will be cold and dry, a meteorologist for Accuweather.com, David Dombek, said. Tomorrow may see wet snow or rain in the morning, though it will not accumulate on the ground. The morning will be breezy, but the winds will be howling by evening, Mr. Dombek said.

Wind has been a special concern for the parade since a careening Cat in the Hat balloon knocked over a lamppost and injured four people in 1997.

Mr. Veras said that Macy’s decides whether to ground any balloons in consultation with the New York Police Department only minutes before the start of the parade.

The Police Department announced several Thanksgiving street closures yesterday, including the route of the parade along Central ParkWest from 77th Street to Columbus Circle, along Broadway from Columbus Circle to 34th Street, and west on 34th Street to Seventh Avenue.

The Port Authority estimates that more than 1.5 million people will move through the city’s three airports during the holiday period that begins this morning and continues through Sunday. More than 3.4 million will use the agency’s bridges and tunnels, the Port Authority expects.

Sixty extra trains began traveling Amtrak’s Northeast Corridor, between Washington and Boston, yesterday, a spokesman, Cliff Black, said, according to Bloomberg News. They will continue through Monday to meet holiday travel demands.

Amtrak expects to carry 125,000 passengers nationwide today, compared with 69,000 on an average Wednesday, according to the Bloomberg wire.

Many New Yorkers will spend their Thanksgiving volunteering for charity.

The Food Bank for New York City will distribute 10,500 turkeys throughout the five boroughs, which will feed 160,000 people on top of the 250,000 people the organization feeds each day. The Food Bank supplies food to hundreds of soup kitchens, food pantries, shelters, and low-income day care centers in New York City.

Citymeals-on-Wheels will deliver more than 12,000 meals to homebound seniors in time for Thanksgiving dinner.

God’s Love We Deliver will prepare and deliver close to 2,200 Thanksgiving feasts of roast turkey, pumpkin bisque, and cornbread stuffing, to 1,600 people living with serious illnesses including AIDS, cancer, and lupus. The group’s clients, who receive daily meals free of charge, can request a guest meal if they plan to have company for Thanksgiving dinner. The group also feeds their clients’ dependents and caregivers.

City Harvest will have collected 300,000 pounds of food in time for the holiday. Tonight it will stage a “midnight rendezvous” with seven trucks that the grocery delivery company Fresh Direct has stationed throughout the city with extra components of its Thanksgiving meals, in case anything breaks or is missing from a customer’s order. Starting at 11:30 p.m. and into the morning, City Harvest volunteers will pick up whatever food hasn’t been needed and distribute it to agencies like the Bowery Mission.

The director of food development for City Harvest, Jennifer McLean, estimated that Fresh Direct would donate 6,500 pounds of gourmet food.

“The best stuff – beautiful food – is going to people who could never afford to order from Fresh Direct,” Ms. McLean said.